1. Field of the Invention
The present invention relates to an image pickup method and system and more particularly to an image pickup method and system which are suited for picking up an image of a rapidly moving object.
2. Description of the Prior Art
In connection with the use of solid-state imaging devices such as CCD's (charge coupled devices) in television cameras, it has been proposed to make the integration period of the solid-state imaging device shorter than the field (or frame) period of the television signals by changing the method or manner of driving the imaging device. As an example, in the Japanese patent application No. 61098/1983 (laid open dated Oct. 22, 1984, No. 185475/1984 corresponding U.S. patent application Ser. No. 596,404, filed Apr 3, 1984), there is disclosed a drive method by which, in a frame-transfer type CCD, charges generated at an imaging part of the CCD are forcibly eliminated or cleaned off from the imaging part by being vertically transferred to a storage part at a particular time during the field period. The remainder of the field period is then utilized as a substantial integration period.
According to the above described method, in an NTSC television system, though the normal integration period is 1/60 second, this integration period can be changed to 1/120 or 1/500 second. With this integration period shortening method, the aperture size does not need to be decreased when a large quantity of incident light reaches the imaging part of the CCD. On the other hand, if the object brightness does not change, the diaphragm aperture is automatically opened with the shortened integration period; and an out-of-focus effect, in which only the focused object is sharply imaged, is obtained due to the shallowed depth of field. Also, with shortened integration period it is possible to pick up the image of a rapidly-moving object without any blur.
However, if the substantial integration period is shortened, the diaphragm must be opened more than during the normal integration period, in order to gain a video signal level equal to the level obtained in the normal integration period (1/60 second), so thataa large quantity of light easily enters the lens. Consequently, charges are easily generated in the CCD image part, making the image prone to blooming.
The prior art also includes drain type anti-blooming arrangements in CCD3 s which cause excess accumulated charges in various cells to be drained away from the device so that the excess charge does not flow into adjacent cells. The prior art further includes control signal responsive anti-blooming means for CCD's which operate to produce charge reductions in particular cells of the CCD according to the control signal.